Frankly I never thought it could happen. By which I mean, I thought Mickey Spillane was one of those guys who would live forever on sheer... whatever it was he had. And yet while his stuff could be kind of appalling, there was no doubt about its power, or its influence. It's hard to imagine Donald Hamilton's Matt Helm, for example, without the example of Mike Hammer. The idea that a guy could commit such brutal violence, be so amoral about committing violence, and still be the hero and (sort of) on the right side of the law, is something that Spillane has given to our popular culture, and for better or for worse -- sometimes for better, I think -- it's here to stay.
I've linked to it before, but this would be an appropriate time to re-link to Jean Kerr's re-imagining of the Mike Hammer stories in a high-culture setting, "Don Brown's Body."
Update: Sarah has a link to a good obit and she'll have more links and info on her blog tomorrow.